Shock absorbing linkage mechanism



June 25, 1968 L. G. KAPLAN SHOCK ABSORBING LINKAGE MECHANISM 2Sheets-Sheet 1 Original Filed Dec. 25, 1957 INVENTOE Lows G %PLAN 4' 3%MA1- TY.

June 25, 1968 (5, KAPLAN Re. 26,41 7

SHOCK ABSORBING LINKAGE MECHANISM 2 Sheets-Sheet. 2

Original Filed Dec. 25. 1957 s3 I 37 f 2 35 Ioovam'ora Lows PLAN ATTY.

United States Patent Oflice Reissuecl June 25, 1968 26 417 SHOCKABSORBING iINKAGE MECHANISM Louis C. Kaplan, Evanston, Ill., assignor toCullen- Friestedt Company, Chicago, III., a corporation of IllinoisOriginal No. 2,959,411, dated Nov. 8, 1960, Ser. No. 704,385, Dec. 23,1957. Application for reissue Aug. 7, 1967, Ser. No. 663,461

1 Claim. (Cl. 26771) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE The present invention relates to lifters foruse in handling and moving or transporting metallic sheets and likearticles from place to place The invention is particularly concernedwith lifters of the type which [are] is adapted to be hoisted and movedfrom one place to another by a crane or overhead hoist. A lifter of thischaracter has as its principal components or parts: (I) a supportingelement having means thereon whereby it may be attached to a hook orother connecting device on the operating end of [a] the crane or [a]hoist with which the litter is to be used; (2) a pair of opposedhorizontally elongated, complemental jaws which are pivotally connectedto the supporting [elements] element so that they are capable ofswinging toward and away from each other into and out of engagement withthe side margins of the sheets or other articles to be lifted; (3) areversible electric motor which is mounted on the supporting element;and (4) a train of motor actuated gearing which is associated with, andcarried by, the supporting element, operates when driven in onedirection to shift the jaws apart and when driven in the oppositedirection to move the jaws toward each other into gripping relation withthe sheets or other articles and includes a speed reducing unitoperativcly connected between the drive shaft of the motor and ahorizontal rock shaft positioned under the supporting element andoperatively connected through linkage mechanism to the jaws. A litter ofthis character [has been] is shown and described in [the] United StatesPatent to Hooker No. 2,695,809, dated Nov. 30, 1954 and entitled"Litter," and the present invention is designed as an improvement oversuch a litter construction.

In the above-mentioned patent to Hooker there [has been] is disclosed alost motion linkage mechanism which extends between the jaw-actuatingrockshaft and one of the two cooperating jaws. the lost motion mechanismbeing provided with a take-up spring which is adapted to becomecompressed when the two jaws are brought into engagement with the sidemargins of the sheets or other articles which are to be lifted or wheneither jaw is subjected to shock or impact tending to limit its inwardtill swinging motion. The take-up spring associated with the lost motionlinkage mechanism shown and described in the above-mentioned Hookerpatent serves normally to take up lost motion in one direction only andthus the lost motion connection is etiective to assimilate shock onlywhen there is an impact tending to limit the inward swinging motion ofthe jaws. In the event of an impact tending to limit the outwardswinging motion of the jaws. the lost motion connection is rigid andthus no protection against shock is offered to either the speed reducingunit or the electric motor which drives the same. Such shock may be theresult of the jaws becoming wedged between two adjacent objects duringtheir outward swinging motion, or it may 'be the result of inadvertentcontact between the outer surface of one of the jaws and an adjacentobject, either during outward swinging movement of the jaw or duringtransportation of the unloaded lifter assembly by the hoist mechanismfrom one location to another.

It is among the principal objects of the present invention to provide alifter of the type briefly outlined above and shown in theabove-mentioned patent to Hooker and in which the actuating rock-shaftfor the lifter jaws is operatively connected to one of the jaws by oneor more double-acting springbiased lost motion linkage mechanismscapable of absorbing any sudden shock which may be applied to the litterjaws from the outside or from the inside of the jaw structure duringoutward or inward swinging movements of the jaws respectively, and alsocapable of absorbing shock which may be entered by the jaws duringtransportation of the lifter when the jaws are empty, whether the shockbe occasioned by an inside or an outside blow on the lifter jaws.

Other objects and advantages of the invention, not at this timeenumerated, will become more readily apparent as the nature of theinvention is better understood.

In the accompanying two sheets of drawings forming a part of thisspecification a preferred embodiment of the invention [has been] isshown.

In these drawings:

FIG. 1 is a fragmentary vertical sectional view taken through a litterassembly in the vicinity of the power actuated gear driving mechanismtherefor and showing the improved linkage mechanism of the presentinvention operatively applied thereto;

FIG. 2 is a side elevational view of a link assembly employed inconnection with the present invention;

FIG. 3 is a sectional view taken substantially along the line 33 of FIG.1;

FIG. 4 is a sectional view similar to FIG. 3 but showing the linkassembly in an extended position;

FIG. 5 is a sectional view similar to FIGS. 3 and 4 but showing the linkassembly in a contracted position;

FIG. 6 is a sectional view taken substantially along the line 6-6 ofFIG. 3; and

FIG. 7 is a circuit diagram for the electric motor associated with thelifter and illustrating certain safety features employed in connectionwith the invention.

Referring now to the drawings in detail and in particular to FIG. 1, theimproved linkage mechanism of the present invention is shown as beingoperativelv applied to a lifter of the general type shown and describedin the above-mentioned patent to Hooker, No. 2,695,809. Only suchportions of the lifter assembly as are pertinent to the operation of thelinkage mechanism [have been] are illustrated herein and for a detaileddescription of the entire mechanism and its mode of operation, referencemay be had to [this] said patent. The lifter involves in its generalorganization an elongated supporting element 10, a pair of jawassemblies 11 and 12, a reversible electric motor 14, and a power train16 extending between the motor and jaws for conjointly shifting thelatter toward and away from each other in response to operation of themotor.

The supporting element is in the form of a horizontally extending I-beamhaving horizontal top and bottom flanges 18 and 19, respectively,connected together by a vertically extending web 20. At suitable spacedpoints along the I-beam 10 there [are] is provided a series of spacedattachment or pivot lugs, only one of which [has been] is disclosedherein and designated at 22. Each lug 22 has pivotally connected theretoon opposite sides thereof one of the [pairs] pair of jaw assemblies 11and 12, each jaw assembly being attached to the lug by means of a pivotpin 24. The pivot lugs 22 fit between the top and bottom flanges 18 and19 of the supporting element 10 and are welded as at 26 in positionthereon. The two jaw assemblies 11 and 12 are substantially identical inconstruction and each is in the form of a composite assembly includingan upper or proximate jaw section 28 and a lower or distal jaw section30 hingedly connected as at 31 to the upper section.

The upper jaw section 28 has its upper end region curved inwardly andthe section is comprised of a pair of laterally spaced flat metal bars32 and 34 (see also FIGS. 3, 4 and 5). The upper ends of the bars 32 and34 straddle the pivot lug 22 and the pivot pin 24 extends through thethree thicknesses of metal involved. The lower section 30 is in the formof a single fiat metal bar 36, the upper region of which projectsbetween the bars 32 and 34, with the hinge pin 31 extending through thethree metal thicknesses. The extreme upper end region of the bar 36 isin the form of a toothed sector 38 capable of swinging movement betweenthe bars 32 and 34 of the upper jaw section 28 and capable of beinglocked in any desired angular position of adjustment by means of a lockbar 40 which passes through a pair of slots 44 provided in the bars 32and 34 and which is capable of being selectively received in a series ofnotches 46 formed on the periphery of the sector 38. The lock bar andsector arrangement just described provides a convenient means wherebythe angular position of the lower jaw section 30 may be adjustedrelative to the upper jaw section 28 to decrease or increase theeffective span of the two jaws to adapt the jaws to articles of varyingwidth. The lower jaw section 30 of each jaw assembly 11 or 12, as thecase may be, are cross-connected by means of horizontally extendingbox-section type members 49, the ends of which are welded or otherwisesecured fixedly to the central regions of the flat bars 36. The lowerends of the lower jaw sections 30 carry opposed angle bar grippingmembers 50. The electric motor 14 by means of which the jaws 11 and 12are actuated is preferably of the reversible series wound direct currenttype. The motor includes a casing 51 having a mounting flange 52 securedby bolts 54 to the underneath side of the horizontal lower flange 19 ofthe supporting element 10. The motor has operatively associatedtherewith a gear reduction mechanism 56 having an output shaft 58carrying a pinion 60 constituting one element of the previouslymentioned power train 16.

The power train 16 which extends between the Output shaft 58 of the gearreduction device 56 and the jaws 11 and 12 is comprised of a set ofgearing including the pinion 60 and a linkage mechanism, the latterconstituting one of the important features of the present invention. Thegearing, in addition to the pinion 60, comprises a gear segment. 62which meshes wilh the pinion 60. The gear segment 62 is keyed orotherwise secured to a rude shaft 64 suitably mounted in bearings 66provided on a bracket 68 which depends from the underneath side of theflange 19 [associated with] 0 the supporting element 10. Also keyed orotherwise secured to the rockshaft 64 [are] is a pair of bifurcatedcrank arms 70 and 72 which extend radially outwardly from the rock-shaft64 generally in opposite directions. The distal end of the crank arm 70is pivotally connected as at 74 to one end of a thrust link 76, theother end of the link 76 being pivotally connected as at 78 to a medialregion of the upper jaw section 28 of the jaw assembly 12. The distalend of the crank arm 72 is pivotally connected by a horizontal pivot pin80 to one end of a spring biased lost-motion link assembly designated inits entirety at 82, the other end of the link assembly 82 beingpivotally connected by a horizontal pivot pin 84 to a medial region ofthe upper jaw section 28 of the jaw assembly 11.

The arrangement of parts thus far described, with the exception of thespecific character of the link assembly 82, is purely conventional andno claim is made herein to any novelty associated with the same. For amore detailed description of the motor 14, gear reduction device 56, thespecific mounting means for the motor and its gear reduction device andother mechanism which may be associated with the lifter assembly andwhich is not pertinent to the present invention, reference may be had tothe above-mentioned Hooker patent for a full disclosure of thesedetails. The invention of the present application resides rather in thenovel construction and arrangement of parts associated with the springbiased lost motion link assembly 82 which will now be described indetail and its operation subsequently set forth.

The link assembly 82 involves in its general organization fourrelatively movable parts or assemblies, together with a preloadcompression spring which serves to maintain these assemblies in a normalor intermediate position when the link assembly 82 as a whole is in itsfree state, or when compressional or tensional forces below apredetermined minimum are applied to the ends of the assembly. Thecompression spring by means of which these four parts or assemblies arenormally held in their neutral or inoperative position is designated inits entirety at 86.

The four parts or assemblies set forth above include an inner linkmember 100, an outer encompassing link member 102, a slide member 104,and thrust collar 106. The inner link member is of a composite natureand comprises a cylindrical rod 108, one end of which is threaded as atand is threadedly received in a thread ed bore 112 of a socket member114. One end of the socket member 114 is welded as at 116 to a sleeve 18which, in combination with the pivot pin 84, provides the pivotalconnection whereby one end of the link assembly is connected to themembers 32 and 34 of the upper jaw section 28 of the jaw assembly 11.The outer link member 102 may be in the form of a casting providing apair of parallel fiat bar-like arms 120, the right hand ends of which,as viewed in FIGS. 2, 3, 4 and 5, are connected together by a sleeveportion 122 which surrounds and is slidable on the socket portion 114 ofthe inner link member 100. The left hand ends of the bar-like arms areconnected by means of the pivot pin 80 to the bifurcated crank arm '72.The upper and lower edges of the arms 120 are each formed with lugs 124providing shoulders or abutments 126, the function of which will be setforth presently.

The slide member 104 is in the form of a relatively thick plate or block(FIGS. 3 and 6) having a central opening therethrough, through which therod 108 extends and in which opening it is slidable. The opposite edgesof the [plate] block 104 are notched as at 132 to provide pairs of ears134 which straddle the members or arms 120, respectively. so that theblock 104 is constrained to slide longitudinally on these arms. The

collar 106 surrounds the rod 108 in the immediate vicinity of the socketmember 1114 and the rod 108 is slidable through the collar for purposeswhich will also be made clear presently.

Still referring to FIGS. 2, 3, 4 and 5, the compression spring 86 is ofthe helical variety and, in its free state, is provided with a series ofopen or spaced convolutions to allow for limited compression of thespring endwise in the usual manner of operation of such compressingsprings. The spring 86 surrounds the [inner] rod 108 and bears at oneend against one side of the slide member or block 104 and at its otherend against the collar 106. The length of the compression spring is suchthat it normally maintains the collar 106 seated against an internalshoulder 136 provided at the juncture between the sleeve portion 122 andthe arms 120, while at the same time maintaining the slide block 104against the shoulders 126 atlorded by the integral lugs 124 on the arms120. The left hand end of the rod 108 has mounted thereon a limit collar138 which is anchored in position by a set screw 140 and the distancebetween the collar 138 and socket member 114 on the rod 108 is suchthat. in the normal position of the parts as shown in FIG. 3, thecompression spring 86, will through the medium of the collar 106, forcethe slide block 104 and collar 106 outwardly away from each other inopposite directions whereupon the collar 106 will bear against theextreme end of the socket member 114 and cause the entire compositeinner member 100 of the assembly 82 to be moved to the right as shown inFIG. 3 until such time as the limit collar 138 bears against the slidemember 134. The spring 86 thus maintains the four relatively movableparts or elements 100, 102, 104 and 106 of the assembly in the positionsin which they are illustrated in FIG. 3, this being the neutral positionof the assembly when the same is under neither compressional nortensional forces.

In the operation of the link assembly 82, when the rock-shalt 64 isturned in a clockwise direction as viewed in FIG. 1, the crank arm 70will force the link 76 to the right, thus swinging the jaw 12 outwardlyabout its pivotal axis 24. At the same time the crank arm 72 will forcethe link assembly 82 to the left thus swinging the jaw 11 outwardlyabout its pivotal axis 24. Conversely, as is obvious, when therock-shait 64 is turned in a cnunterclocrwise direction, the linkagemechanism will be actuated to draw the jaws 11 and 12 inwardly towardeach other.

During outward swinging of the jaws 11 and 12 under the motivatinginfluence of the electric motor 14, operating through the gear reductiondevice 56, output shaft 58 thereof, pinion 60, gear segment 62, crankarms 70 and 72, and links 76 and 82, it the jaws 11 and 12 should becomewedged between two opposed adjacent objects, or if one of them shouldstrike an adjacent massive object. counter-torque will be applied to therock-shaft 64 through the link assembly 82 and such counter-torque whenapplied to the shaft 64, will tend to compress the link assembly 82. Asshown in FIG. 5, the application of compressional forces to the oppositeends of the link assembly 82 will cause the socket member 114 to slideinwardly through the sleeve portion 122 of the outer link member 102,thus forcing the collar 106 to the left, as viewed in this figure, andcompressing the spring 86 between the collar 106 and slide member 104which is held against the shoulders 126 of thc integral lugs 124 on theside bars 120. Movement of the socket portion 114 in this manner willcause the rod 108 to be slid to the left through the slide member 104 sothat the limit collar 138 moves away from this slide member. Theeffective length of the link assembly 82 thus becomes shortened and thespring 86 assimilates the shock which otherwise would be imparted to thepower train 116 leading to the motor 14 where conventional rigid linkconstructions are conccrned. When the compressional force on the linkassembly 82 is relieved, the parts will be restored to their neutralposition as shown in H6. 3.

When internal shock is encountered by the jaws 11 and 12, as, forexample, when the angle bar gripping members 50 engage the side marginsof a stack of sheets or other objects to be lifted during inwardswinging movement of the jaws 11 and 12 under the influence of the motor14, such inward swinging motion of the jaws is immediately arrested andtensional forces are applied to the link assembly 82 tending to expandthe same longi tudinally. When this occurs the inner link part will bemoved to the right as viewed in FIG. 4 so that the limit collar 138 willforce the slide block 104 to the right along the members 120 on which itis slidable and the spring 86 will be compressed between this slideblock and the collar 106. The collar 106 will bear against the internalshoulder 136 and thus receive the end thrust of the spring 86. It willbe seen, therefore, that the spring 86 assimilates any shock incidentupon interruption of the inward swinging movement of the jaws 11 and 12.

In the single claim which follows this specification: the "firstelement" is the link member 102; the "first slop shoulder on said firstelement" is one of the shoulders 126; the second element" is the innerlink member 100; the second stop shoulder on said first element" is theinternal shoulder 136; the third element" is the slide member 104; thefirst stop shoulder slr'da'ble on said first element is the inner end ofthe soc/re: member 114; the second slop shoulder on said second element"is the limit collar I38; and the "fourth element" is the thrust collar106.

In order to reduce the flow of current through the electric motor 14when the movement of the jaws l1 and 12 is interrupted, during outwardswinging movement thereof, as previously outlined, a limit switch ismounted on one of the arms 120 of the outer link member 102. The limitswitch 150 is provided with an actuating finger 154 which is positionedin the path of movement of the collar 138 which moves to the leftrelative to the arm 120 as seen in H6. 3 when the spring 86 iscompressed under the influence of compressional forces acting on theopposite ends of the link assembly 82. The limit switch 150 hasassociated therewith a normally open pair of contacts 158 (FIG. 7),adapted to become closed under the influence of the actuating finger154. The circuit connections for the limit switch 150 will be set forthsub sequently.

The reversible electric motor 14 is of the series wound, direct currenttype in which reversal of the direction of current flow through themotor armature will effect reversal of the direction of rotation of themotor shaft, and consequently of the output shaft 58 of the gearreduction mechanism 56. Such selective reversal of the current tlowthrough the armature circuit of the motor 14 will control the directionof movement of the lifter jaws 11 and 12. in order to prevent excessivemotor speeds during inward swinging movements of the jaws l1 and 12under the influence of gravitational forces acting upon the jaws, meansare provided whereby full line current will be applied to the armaturecircuit with the current flowing through the circuit in a direction tocause clockwise rotation of the rock-shalt 64 and consequent openingmovement of the jaws 11 and 12. The motor 14 will thus be driven underfull power. However, when the direction of current flow through thearmature circuit is reversed so that the power train 16 is actuated tocause counterclockwise rotation of the rock-shaft 64 to effect closingmovement of the jaws 11 and 12, automatically operable means areprovided for introducing a resistance element into the armature circuitso that the motor will be driven under reduced power. The circuitdiagram of FIG. 7 illustrates schematically the manner in which such aresistance is automatically introduced into the armature circuit of themotor and it also illustrates the manner in which the limit switch 150is capable of interrupting the flow of current through the armaturecircuit.

Referring now to FIG. 7 in detail, full line current may be applied tothe armature circuit of the motor 14 from the positive side of the line,through a reversing switch 160, leads 2], 23, motor 14, leads 25, 27, apair of normally closed contacts 29 associated with a relay magnet M,leads 31, 33, 35, and reversing switch 160 to the negative side of theline. Current flowing through the armature of the tnotor 14 in thisdirection will move the rock-shaft 64 in a clockwise direction so as tocause opening movements of the jaws 11 and 12, as previously described.

When the reversing switch 160 is operated to reverse the direction ofcurrent flow through the armature of the motor 14, a circuit will existfrom the positive side of the line through the reversing switch 160,leads 35, 37, relay magnet M, lead 39, a unidirectional device SR whichmay be in the form of a selenium rectifier, leads 47, 49, 21, andreversing switch 160 to the negative side of the line. Energization ofthe relay magnet M will cause opening of the contacts 29, thusestablishing a circuit extending from the negative side of the line,through the reversing switch 160, leads 35, 33, 51, resistance R, leads53, 25, armature of the motor 14, loads 23, 21 and reversing switch 160to the negative side of the line. The ohmic value of the resistor R maybe selected according to engineering requirements to produce a desiredvoltage drop thereacross and reduce the current flow through the motorarmature to such an extent that overspeeding of the motor 14 under theinfluence of gravitational forces acting upon the jaws l1 and 12 duringclosing movements there of will be avoided.

The normally Open pair of contacts 158 associated with the previouslydescribed limit switch 150 on one of the arms 124 of the outer linkmember 102 is disposed in shunt relationship with the unidirectionaldevice SR. Thus, when the actuating finger 154 is engaged by the collar138 and the contacts 158 become closed, the unidirectional device SRwill be bypassed and a shunt circuit passing through lead 43, contacts158, lead 45 and magnet M will be completed, thus opening the contacts29 and restoring the circuit through the resistor R and motor armatureso as to reduce the power output of the motor [10] 14. Such a conditionwill obtain, for example, when compressional forces are applied to theends of the link assembly 82 due to the lifter jaws becoming wedgedbetween two adjacent objects during opening of the jaws under full motorpower, as previously described.

A preferred embodiment of the invention [has been] is shown in thedrawings and described herein, but it should be understood that theinvention is not limited to the specific disclosure made. For example,although in FIG. 1 only one of the improved lost motion link assemblies82 has been shown in association with the gear segment 62, the assemblybeing connected to the jaw 11, it will be understood that the thrustlink 76 may be replaced by an assembly such as the lost motion linkassembly 82 having its opposite ends connected between the gear segment62 and jaw 12. The appended claim should, therefore, be construed asbroadly as the prior art will permit.

Having thus described the invention what I claim as new and desire tosecure by Letters Patent is:

[1. A compressible and extensible shock absorber link assemblycomprising four relatively movable link elements capable of axialshifting movement in opposite directions relative to one another andincluding a first element having means for attaching the same to one ofsaid arms, a first stop shoulder on said first element facing said otherarm, a second element slidable on said first element, having means forattaching the same to the other arm, a second stop shoulder on saidfirst element facing said one arm, a third element slidzrhlc on saidfirst element llLllWL'Cll the lwu stop shoulders on the latter and beingengageable with the first stop shoulder,

said second element being slidable through said third element, a firststop shoulder slidable on to said first element, interposed between saidthird element and the second stop shoulder on the first element andengageable with said latter stop shoulder, a second stop shoulder onsaid second element on the side of the third element remote from saidother arm, facing the latter arm and engageable with said third element,and a compression spring surrounding said second element and hearing atone end against said third element and hearing at its other end againsta fourth element, said spring normally urging said fourth elementagainst said stop shoulder on the first element and urging the thirdelement against the second stop shoulder on the second element, saidfirst stop shoulder on said second element being engageable with thefourth element when compressional forces are applied to the linkassembly by said attaching means to compress said spring against saidthird element, said second stop shoulder on the second element beingcngageable with said third element to compress said spring against saidfourth element when tensional forces are applied to the link assembly bysaid attaching means, said first element being in the form of a pair ofspaced parallel bars connected together at the end thereof adjacent saidother arm by an integral collar portion, said second element being inthe form of a cylindrical rod slidable through said collar portion, saidthird element being in the form of a block extending across said barsand having notches in the latter side edges thereof within which saidbars are slidable, said block also having a hole therethrough throughwhich said rod extends and in which it is slidable, said means forattaching said first element to said one arm including a cylindricalsocket member carried by said one arm and having a threaded socketformed therein and in which socket one end of said cylindrical rod isthreadedly received] 2. A compressible and extensible shock absorberlink assembly adapted for operarit'ely connecting two relatively movablearms and comprising a first clement having means for attaching the someto one of said arms, said first element being in the form of a pair ofspaced parallel bars connected together or the end thereof adjacent tothe other arm by an integral collar portion, a second element in theform of a cylindrical rod slitiablc through said collar portion andhaving means for attaching to said other arm including a first stopshoulder adapted for carrying by said other arm and having a threadedsocket formed therein and in which socket one end of said cylindricalrod is thrcadedly received, a first stop shoulder on said first clementfacing the other arm, a second stop shoulder on said first clementfacing said one arm, a third element in the form of a block extendingacross said bars and having notches in the latter sic/e crigcs thereofwithin which said bars are slidable, .micl block engaging said firststop shoulder and having a hole thcrcthrough through which said rodextends and in which it is slidablc, a fourth clement sliilable on saidscc- 0nd element and interposed between said third element and thesecond stop shoulder on the first element and engageable with saidlatter stop shoulder, a second stop shoulder on said second element onthe side of the third element remote from the olh-er arm, facing thelatter arm and engflgeable with said third element, and a comprciw .sionspring surrounding said second element and bearing at one end againstsaid third element and bearing at its other end against said fourthelement, said spring normally urging said fourth clement against saidsecond stop shoulder on the first element and urging the thirrl elementagainst said second stop shoulder on the second element, said first stopshoulder on said second element being engageable with said fourthelement when compressional forces are applied to the link assembly bymid attaching men/m to compress twirl spring ugh/us! .mirl lllll'tltlr/Hr'nl, suiil .rccond stop shoulder on the second element being 9 1Oengageable with said third element to compress said 1,757,164 5/ 1930Blake ct a1. spring against said fourth element when tensional forces1,837,192 12/1931 Barrows et :11. are applied to the link assembly bysaid attaching means. 2,360,740 10/ 1944 Sturdy.

2,372,214 3/ 1945 Loepsinger. References Cited 5 2,526,373 10/ 1950LeClair. The fo11owing references, cited by the Examiner, are of2,695,809 11/1954 Hookerrecord in the patented file of this patent orthe original FOREIGN PATENTS patent. 4

UNITED STATES PATENTS 412838 7/1910 France- 1,137,145 4/1915 Krarup.ARTHUR L. LA POINT, Primary Examiner.

,460,771 7/1923 Stoner. 1,621,011 3/1927 Harvey et a1. EUGENE BOTZ Ewmm"1,705,728 3/1929 Harvey. S. KRAWCZEWICZ, Assistant Examiner. 1,717,2196/1929 Jones. 15

